Allot steel



April 14, 1.942- G. sELMl ETAL Re- 22,072

` ALLOY STEEL Original Filed July 12, 1940 5 Sheets-Sheet 1 C. N. H 5. Si. Ni. Ck. V. No. STEL-A ./J .66 .021.021 .l .os .4a

R. .OS

ENS/L E DPA w /630 /630 /650 [630 /630 I 500 600 700 600 `.900 /000 l/OO /600 /N WATER COOLED ON /l/A.

ATT

April 14, 1942. G. SELMI ETMl Re.' 22,072

ALLOY STEEL Orznal Filed July 12, 1940 3 Sheets-Sheet 2 'April 14, 1942. L.. G.' si-:LMI I ET 1. Re- 22,072

ALLOY STEEL Original Filed July 12, 1940 3 Sheets-Sheet 3 Reinued Apr. 14, 1942 lUNITED STATES PATENT OFFICE burger, Dearborn,

Mich., assigner: to- Great Lakes Steel Corporation, Ecorse. Mich., a corporation oi' Delaware original No. 2,234,130.

dated March 4, 1941, Se-

rial No. 345,227, `Iuly 12)A4 1940. Application lor reissue February 2, 1942, Serial No. 429,344

3 Claims.

This invention relates to steel and a composition oi same particularly adapted to rolling into commercial shape of varied size and form such that the physical properties of the material of such variable sizes and forms do not depart appreclably from the optimum values within a range ordinarily covered by that class of steel which has become known to the trade as low alloy high tensile steels. The invention also relates to a steel of the aforesaid composition capable of being heat treated in varied shapes and sizes to predetermined but narrow ranges of hardness distributions or other physical properties dependent upon such hardness distributions.

Objects of the invention include the provision of an improved high tensile steel; the provision of an improved high tensile-steel having a maximum oi 0.50% molybdenum; and the provision oi an improved high tensile having a maximum of 0.25% carbon.

Other objects of the invention include a provision for a steel whose composition shall ybe variable within deiinite ranges in accordance with the size and shape of the nnished steel: the provision of an improved high tensile steel capable of being heat treated to predetermined but narrow ranges of hardness distribution or other physical properties dependent thereon.

The above being among the objects of the present invention, the same consists in a certain new and useful alloy steel and particularly to one of new and novel analysis as well as to articles formed therefrom whereby to impart to the same certain desirable characteristics, to be hereinafter described and then claimed, having the above and other objects in view.

In the accompanying drawings:

Fig. l is a chart illustrating the properties ofthe steel of the present invention after heat treatment;

Fig. 2 is .a chart illustrating the hardness of the steel of the present invention across quenched and tempered sections at various draw- I ing temperatures; A

Fig. 3 is a chart illustrating the hardness at various points through a one-haii inch plate formed of the steel ot the present invention and which plate has beenV carburized on one face;

Fig. 4 is a photograph of a plate of steel having an analysis conforming to the present invention and having the surf ace thereof carburized and hardened, after having been hit with .30 caliber standard service bullets and .30 caliber armor piercing bullets:

(Cl. 'l5-128) that shown in Fig. 4 and similarly carburized and hardened but-lacking the molybdenum content of the steel of the plate shown in Fig. 4 and illustrating the eiect of the same oi .30 caliber standard service bullets; and, A

Fig. 6 is a chart illustrating the varying molybdenum content in the4 steel of the present invention according to the sectional thickness of the part made therefrom.

l As is well known. many compositions of steel produced with laboratory facilities can be bal- .,iiriced chemically so as to produce physical properties within a given range. Such compositions may or may notbe capable of yielding these same desired properties when subjected to the conditions prevailing in actual commercial steel manufacturing. Rolling temperatures, rate 0f cooling after rolling together with the size and shape of the finished material are the main variables affecting this condition.

In the specific case of those steels which have become known to the trade as low-alloy high tensile steels, ln generalthey are required to possess' tensile properties approximately as followsz,

Yield point 50.000 p. s. i. min. Tensile strength. 70,000 p. s. i. min. `Per cent elongation in 2" 25% min.

Many comparatively simple analyses are capable of producing tensile properties in the aforesaid range when rolled hot to comparatively thin gauges, by controlling finishing 'temperatures and by the use of copious application of water to the steel on the run out table or cooling bed after the steel has passed through the last stand of rolls. When the gauge or thickness of strip or plate, for example, increases, such procedures become rapidly less effective and tensile properties 40 lower than the above minima are obtained from the steel in its rolled condition.

In the past few years the requirements of low alloy high tensile steels have increased swiftly. They were originally intended for relatively simple fabrication methods. Today such steels must weld by all commercial welding processes as easily as mild carbon steels; they must be equal to or better than mild carbon steels in the matter of deep drawing objects therefrom; they mustbe capable of responding to the ordinary methods of heat treatment and case hardening; they must possessgood notched bar resistance at both normal and sub-normal temperatures, high fatigue resistance, especially fatigue resistance at Fig. 5 is a View of a piece of steel similar to 55 notches or other stress-raisers which may reside within the body of the steel itself. The steel should have ali contained nitrogen ilxed in inactive forms and be free from strain or quench aging. The steel must vnot be air hardening at any carbon content and should possess no precipitable elements capable of impairing its physical properties'upon stress relieving after Welding or normalizing. This imposing list of properties demanded by modern steel users is due in part to the increasing precision of modern manufacturing and partly to the increased use of technical testing of fabricated structures.

A steel. which will hereafter be referred to as steel A," of the following analysis has been found partly to fulfill the above:

Per cent Carbon .05- .20 Manganese .50- .75 Silicon .70- .90 Chromium .45- .75 zirconium .10.- .15 Phosphorus .03 max. Sulphur .03 max.

The bamn'ce is iron and incidental impurities.

The permissible rolling temperatures are, however. quite narrow on thethinner gauges. On the heavier gauges the cooling rate is too slow to obtain the desired tensile properties in the 11nished material. Moreover the hardenability of the steel is too low to make heat treatment by quenching and drawing eifective for most purposes above about one-half inch diameter round. Moreover. hardness distributions across heat treated sections cannot be controlled to predetermined but narrow ranges except on small or thin shapes.

It has. been found in accordance with the present invention that a steel, hereinafter referred to as steel B," of materially better characteristics than the above mentioned steel, adapting it to the same and also to wider and different fields of use, can be obtained by producing a steel incorporating the same alloying agents as in the steel above mentioned but containing, in addition thereto, small amounts of molybdenum, with or without the further addi- -tion of small amounts of nickel and/or copper. In other words a. steel according to the present invention will have the following composition.-

Per cent Carbon .05- .25 Manganese .50- .'75 Silicon .'10- .90 Chromium .24- .75 Zirconium .10- .15 Molybdenum .02- .50 Phosphorus .03 max. Sulphur .03 max. Nickel Upto .6 }Optional or Copper Up to .3 unavoidable The nickel and copper may be present as residual elements. That is, they may be present in the final steel because of forming an alloying element of the steel scrap employed in the production of the steel of the present invention. Where present as residuals nickel may be present in amounts up to approximately 0.10% and copper in amounts up to approximately 0.14%. Amounts of nickel up to 0.6% and copper up to 0.3% may occur in the alloy of the present invention without materially affecting the properties thereof, the nickel in the higher amounts perhaps adding some toughness, enhancing the heat treatment and reductionl of area to a slight extent, and adding somewhat to the corrosior. resisting properties of the alloy. However, the effects of adding nickel and/or copper up tothe maximum percentages noted will not materially affect the principal characteristics oi the alloy of the present invention, and it may be added or eliminated as desired, and this fact is to be kept in mind in the following specification and claims regardless of whether these two elements, or either one of them. is called for or not. In other words their presence is permissive but notl compulsory.

The steel resulting from this analysis, particularly where properly heat treated, will be found to have all of the desirable attributes or characteristics heretofore listed as required of a steel of this general type under present day re-v quireinents.l

As an example of the effect of added molyb-` denum on the tensile properties of one inchg diameter bar rolled with the same procedure on a fourteen inch merchant mill from 200 tong `basic open hearth heats the following is cited: z

Steel A B Carbon perccnt.. 13 16 l Manganese. .-.do .60 .60 i

Phosphorus ...do 021 .030

phurr... ..do 021 .023 Silicon do. .8l .85 Chromium do.-- .48 5l Zirconium dn.-. .094 i4 Molybdenum. .do None 090 Tensile strength. .p. s. i 000 83,000 Y point .p. s i 50, ooo 61.000 Elongation 2" percent 42 37. 0 Red. area.. ..do 74 70.0

As is evident the tensile strength and yield point are materially raised by the molybdenum addi- 1 Steel A B As is evident, steel A" has approached very nearly the minimum requirements. Upon still slower cooling as by annealing from 1600 F. and cooling to room temperature with the furnace over a two day period, the following results are obtained.

*steel A B Tensile streth ooo 7s. ooo Yield point 50, 500 Elongatinn. percent. 42 36 Red. arca .do 72 0l Finishing temperature Tensile strength Yield point 76,000 to 80.000 51,500 to 54.."00 74,000 to 76,000 50,000 t0 52.000 72,000 to 70,000 45,000 to 49,060

Finishing temperature 1717 to 1720 F.

In the specific case of armor plate applications,

Transverse Longitudinal Tensile strength p. s. i 83. 130 83. 130 Yield point .p. s. i 60,310 o0,3i0 Flongation 2" .percent 32 35 Elongation 4" do 26 26 Elongation 8" ..do 2i 22 Finishing temperature 17 71 F.

Transverse Longitudinal Tensile strength p. s. i 79, 240 7S). 050 Yield point.. 55, 000 53. G50 Eiongation 2". 36 38 Eiongation -i" 2 29 Elongntion 8" do- 21 24 It will be obvious from the foregoing that plate of heavier gauge can be successfully rolled when such steels of the aforesaid classification contain molybdenum in relativehr small proportions.

1 In the` chart shown in Fig. 1 the response of the steel of the present invention to heat treating under the same conditions by the dotted line curves. It will be readily understood from these charts that steels of the analyses of the present invention are capable of yieldingr much higher tensile properties and/or appreciably higher drawing temperatures when heat treated than the similar steel A". Pertinent data is given in Fig. 1 in regard to heat treatment procedure which will readily be appreciated by those skilled in the art.

In the charts of Fig. 2 rdenability curves of the steel of the present invention taken through a round of one inch diameter for various drawing temperatures are shown in full lines and the corresponding hardness curves for the similar steel above referred to as steel A are illustrated in comparative relation by dotted lines. As will be readily understood by those skilled in the art the curves in Figs. 1 and 2 show that much larger sections of steel having the analyses of the present invention can be successfully heat treated than the steel of the prior analysis "A. It might be noted that the steels shown in the charts of Fig. 3 were normalized from 1600 F., re-heated to 1630 F. and they were tempered or drawn fram one hour at the temperatures indicated for the various curves in Fig. 2 sectioned with a water cooled rubber wheel, the surface ground smooth on ne emery paper and the Rockwell C hardness determined at various distance along the radii of the section to obtain the yhardness distribution indicated.

In lthe matter oi carburizing, it has been found that the case strength after heat treating of both steel"A and steel B" to compare with the highest types of alloy steels for carburizing known to the trade. The core hardness istoo low for many purposes in steel A but steel B, due to its greater hardenability, corrects this condition.

quenched in water. Thereafter.

this isla matter of paramount importance. In such applications, one .face of the steel plate to be fabricated into armor plate is carburized.

the plate is heat treated. It is rethe face not .carburized be not too Thereafter, quired that hard for in burized side may effect cracking on the other side and throw splinters or particles off therefrom defeating the purpose of such armor. On the other hand, if the material of the plate in regions not carburized be too soft the case will spall off when struck by a bullet and hence render that area liable to penetration upon being struck by a second bullet thus defeating the purpose of the armor. Illustrations of such spalling will be observed in the photograph of Fig. 5.

The photographs of Figs. 4 and 5 are those of one-half vinch plates carburized in each case to a depth equal to 25% of the thicknesses of the plate on one side only and heat treated. Slices cut from the center of the width of the plate gave a distribution of hardness across the thickness as shown in two cases in Fig. 3. The plate of steel B" when struck with a .30 caliber standard service bullet for Regular Army Springfield .30-06 rifle at 50 feet showed no penetration or deformation as shown in the photograph of Fig. 5. In the case of steel A, however, as shown in Fig. 5, the bullets spalled off the case of high carbon content in an area around the point of striking of about one inch diameter as shown. Further, the plateof steel B is not penetrated by armor piercing bullets from herelnbefore at bullet velocities up to 2900 feet per second. In the plateof steel A the opposite is true.

In the photograph of Fig. 4, the two spots in the upper lefthand corner were produced with ordinary service bullets, the others were produced with armor piercing bullets. In the photograph of Fig. 5 the two spots in the lower lefthand corner show how the case spalled off when struck with regular service bullets.

It will be understood that I do not conne myself to the specific analyses set forth above. For many purposes as for instance, heavy plate where hardnesses in excess .of those shown in the appended charts are required, it will be advantageous to increase both carbon and molybdenum. To attain hardness well over 50 Rockwell C in the centers oi heavy plate, carbon as high as 0.25% and molybdenum up to 0.50% will be required in accordance with the chart shown in Fig. 5, wherein the shaded area covers satisfactory molybdenum ranges at each plate or .other sectional thickness.l The lower part of the shaded area is represented by the equation Percent Mo =0.005+ t y2 where t is the thickness of the plate or thick- Perent M0=.1o+5-`2 (2) Rounds Aon the other hand will preferably have a composition approximately in accordance with Equation 1.

It will be appreciated that by combining the above equations to cover the molybdenum conthat event a bullet striking the carthe same rifle mentioned tent of a steel within the range oi' the present invention and'as indicated in the shaded area, theresulting equation will be:.

Percent Mo-coos to mu-65 to Thus'it will be seen that the thin plate given as .2 inch thickness has'.02% to .04% molybdenum and this amount increases progressively s shown by the black or shaded area. There Ehe molybdenum range reads .50% to 1.00% for inches thickness oi' plate. From the foregoing description it will be seen that the applicants have produced a' low alloy high tensile steel having its alloy element selected, combined and balanced within narrow, but specic and critical ranges, 'whereby the improved steel having the characteristics and accomplishing the objects set forth is provided'. Having thus described our invention, the nature and scope thereof are defined 'in the appended claims, it relationships and ranges specified may be subject to slight or reasonable variation without departing from the spirit of our invention.

What is claimed is: y 1. A low alloy, high tensile steel having properties of welding by commercial processes, deep drawing, high fatigue resistance and freedom from strain or quench aging, containing 0.05%4

to 0.25% carbon, 0.50% to 0.75% manganese, 0.70% to 0.90% silicon, 0.50% to 0.75% chrobeing understood that the particular mium, 0.10% to 0.15% zirconium, phosphorus 0.03% maximum, sulphur 0.03% maximum, from a trace of nickel up of 0.25%, 0.02% to 0.50% molybdenum, and all the remainder being iron and incidental impurities.

2. A low alloy, high tensile steel having the properties of deep drawing characteristics, capable of being welded by commercial processes, high fatigue resistance and freedom from strain aging, containing about 0.15% carbon about 0.70% manganese, about 0.85% silicon, about 0.50% chromium, about 0.14% zirconium, about 0.09% molybdenum, not over 0.03% phosphorus, not over 0.03% sulphur, not over 0.6% nickel, all the remainder being iron and incidental impurities.

3. An article having -a sectional thickness measured in inches, and formed of an alloy steel containing iron and incidental impurities, with 0.05% to 0.25% carbon, 0.50% to 0.75% manganese, 0.70% to 0.90% silicon, 0.50% to 0.75% chromium, 0.10% maximum .of phosphorus, 0.03% maximum oi sulphur, nickel from a trace to 0.25%, and molybdenum in quantities having a predetermined relationship to the sectional thickness of the article and the quantities varying proportionately between limits from 0.02% to 0.04% for .2 inch to 0.25 to 0.50 for 21/2 shown and described.

LUCIANO G. SELMI. CLARENCE L. ALTENBURGER.

to 0.15% zirconium, 0.03%

inches thickness as herein 

